Bachelor of Science, Peking University (2008)
Doctor of Philosophy, Pennsylvania State University (2014)
NAD+biosynthesis is an attractive and promising therapeutic target for influencing health span and obesity-related phenotypes as well as tumor growth. Full and effective use of this target for therapeutic benefit requires a complete understanding of NAD+biosynthetic pathways. Here, we report a previously unrecognized role for a conserved phosphoribosyltransferase in NAD+biosynthesis. Because a required quinolinic acid phosphoribosyltransferase (QPRTase) is not encoded in its genome,Caenorhabditis elegansare reported to lack ade novoNAD+biosynthetic pathway. However, all the genes of the kynurenine pathway required for quinolinic acid (QA) production from tryptophan are present. Thus, we investigated the presence ofde novoNAD+biosynthesis in this organism. By combining isotope-tracing and genetic experiments, we have demonstrated the presence of an intactde novobiosynthesis pathway for NAD+from tryptophan via QA, highlighting the functional conservation of this important biosynthetic activity. Supplementation with kynurenine pathway intermediates also boosted NAD+levels and partially reversed NAD+-dependent phenotypes caused by mutation ofpnc-1, which encodes a nicotinamidase required for NAD+salvage biosynthesis, demonstrating contribution ofde novosynthesis to NAD+homeostasis. By investigating candidate phosphoribosyltransferase genes in the genome, we determined that the conserved uridine monophosphate phosphoribosyltransferase (UMPS), which acts in pyrimidine biosynthesis, is required for NAD+biosynthesis in place of the missing QPRTase. We suggest that similar underground metabolic activity of UMPS may function in other organisms. This mechanism for NAD+biosynthesis creates novel possibilities for manipulating NAD+biosynthetic pathways, which is key for the future of therapeutics.
View details for DOI 10.1074/jbc.C117.795344
View details for PubMedID 28559281
View details for PubMedCentralID PMC5500784
Temporal developmental progression is highly coordinated in Caenorhabditis elegans. However, loss of nicotinamidase PNC-1 activity slows reproductive development, uncoupling it from its typical progression relative to the soma. Using LC/MS we demonstrate that pnc-1 mutants do not salvage the nicotinamide released by NAD(+) consumers to resynthesize NAD(+), resulting in a reduction in global NAD(+) bioavailability. We manipulate NAD(+) levels to demonstrate that a minor deficit in NAD(+) availability is incompatible with a normal pace of gonad development. The NAD(+) deficit compromises NAD(+) consumer activity, but we surprisingly found no functional link between consumer activity and reproductive development. As a result we turned to a comparative metabolomics approach to identify the cause of the developmental phenotype. We reveal widespread metabolic perturbations, and using complementary pharmacological and genetic approaches, we demonstrate that a glycolytic block accounts for the slow pace of reproductive development. Interestingly, mitochondria are protected from both the deficiency in NAD(+) biosynthesis and the effects of reduced glycolytic output. We suggest that compensatory metabolic processes that maintain mitochondrial activity in the absence of efficient glycolysis are incompatible with the requirements for reproductive development, which requires high levels of cell division. In addition to demonstrating metabolic requirements for reproductive development, this work also has implications for understanding the mechanisms behind therapeutic interventions that target NAD(+) salvage biosynthesis for the purposes of inhibiting tumor growth.
View details for DOI 10.1074/jbc.M115.662916
View details for Web of Science ID 000363527300035
View details for PubMedID 26350462
View details for PubMedCentralID PMC4646267
Disruption of cellular metabolite levels can adversely impact development. Specifically, loss-of-function of the C. elegans NAD(+) salvage biosynthesis gene PNC-1 results in an array of developmental phenotypes. Intriguingly, PNC-1 and its functional equivalent in vertebrates are secreted, but the contributions of the extracellular enzymes are poorly understood. We sought to study the tissue-specific requirements for PNC-1 expression and to examine the role of the secreted isoform.A thorough analysis of PNC-1 expression did not detect expression in tissues that require PNC-1 function. Limited expression of both the secreted and intracellular PNC-1 isoforms provided function at a distance from the tissues with phenotypes. We also find that the secreted isoform contributes to in vivo PNC-1 activity. Furthermore, uv1 cell survival has the most stringent requirements in terms of PNC-1 expression pattern or level.Using careful promoter analysis and a restricted expression approach, we have shown that both the secreted and the intracellular PNC-1 isoforms function cell non-autonomously, and that the PNC-1a isoform is functionally relevant in vivo. Our work suggests a model where PNC-1 function is provided cell non-autonomously by a mix of intra and extracellular activity, most likely requiring NAD(+) salvage metabolite transport between tissues.
View details for DOI 10.1002/DVDY.24139
View details for Web of Science ID 000339958400001
View details for PubMedID 24753121
View details for PubMedCentralID PMC5245173
Salvage biosynthesis of nicotinamide adenine dinucleotide (NAD(+)) from nicotinamide (NAM) lowers NAM levels and replenishes the critical molecule NAD(+) after it is hydrolyzed. This pathway is emerging as a regulator of multiple biological processes. Here we probe the contribution of the NAM-NAD(+) salvage pathway to muscle development and function using Caenorhabditis elegans. C. elegans males with mutations in the nicotinamidase pnc-1, which catalyzes the first step of this NAD(+) salvage pathway, cannot mate due to a spicule muscle defect. Multiple muscle types are impaired in the hermaphrodites, including body wall muscles, pharyngeal muscles and vulval muscles. An active NAD(+) salvage pathway is required for optimal function of each muscle cell type. However, we found surprising muscle-cell-type specificity in terms of both the timing and relative sensitivity to perturbation of NAD(+) production or NAM levels. Active NAD(+) biosynthesis during development is critical for function of the male spicule protractor muscles during adulthood, but these muscles can surprisingly do without salvage biosynthesis in adulthood under the conditions examined. The body wall muscles require ongoing NAD(+) salvage biosynthesis both during development and adulthood for maximum function. The vulval muscles do not function in the presence of elevated NAM concentrations, but NAM supplementation is only slightly deleterious to body wall muscles during development or upon acute application in adults. Thus, the pathway plays distinct roles in different tissues. As NAM-NAD(+) biosynthesis also impacts muscle differentiation in vertebrates, we propose that similar complexities may be found among vertebrate muscle cell types.
View details for DOI 10.1016/j.ydbio.2010.11.014
View details for Web of Science ID 000286412800026
View details for PubMedID 21092737
View details for PubMedCentralID PMC3019288
The Hippo-Warts pathway defines a novel signaling cascade involved in organ size control and tumor suppression. However, the developmental function of this pathway is less understood. Here we report that the Caenorhabditis elegans homolog of Warts, Ce-wts-1, plays important roles during worm development. The null allele of Ce-wts-1 causes L1 lethality. Partial loss of Ce-wts-1 function by RNAi reveals that Ce-wts-1 is involved in many developmental processes such as larval development, growth rate regulation, gut granule formation, pharynx development, dauer formation, lifespan and body length control. Genetic analyses show that Ce-wts-1 functions synergistically with the TGF-beta Sma/Mab pathway to regulate body length. In addition, CE-WTS-1::GFP is enriched near the inner cell membrane, implying its possible membrane-related function.
View details for DOI 10.1016/j.febslet.2009.09.002
View details for Web of Science ID 000271286200009
View details for PubMedID 19737560